As an antenna for use in radio communication of MHz band to GHz band such as mobile communication, for example, there has heretofore been known an antenna in which a single sheet-shaped conductive member is used to constitute an antenna radiation member as described in JP(A)2000-4116. In this antenna, a ground surface spacer is disposed between the antenna radiation member and a mount substrate. This is because when a substrate constituting a ground is disposed right under the antenna radiation member, a size of space for accumulating resonance energy decreases, and reception sensitivity of the antenna drops. In this manner, an appropriate size of space has to be held between the antenna radiation member and a ground surface.
Usually, a transmission signal is inputted to the antenna radiation member from a transmission circuit via a transmission-side filter, and a reception signal is outputted from the antenna radiation member to a reception circuit via a reception-side filter. Moreover, a transmission/reception branching unit is disposed between the antenna radiation member and the transmission-side and reception-side filters. When the transmission-side and reception-side filters, the branching unit, and the like are disposed on a main body side of a transmitter/receiver (communication apparatus), miniaturization of a transmitter/receiver main body is constrained. Therefore, it has been proposed that these should be included as an antenna peripheral circuit in an antenna apparatus.
For example, it is described in JP(A)8-288739 that in order to miniaturize the apparatus, a dielectric substrate is disposed under the antenna radiation member via the space having a required size, and the antenna peripheral circuit is built in or attached to the dielectric substrate.
There has been a demand for further miniaturization of the antenna apparatus for use in mobile communication and radio LAN. However, in the above-described conventional structure in which the dielectric substrate is disposed under the radiation member, it is necessary to dispose a predetermined distance between the dielectric substrate and the radiation member. Additionally, a thickness of the dielectric substrate is further added, and therefore the antenna apparatus cannot sufficiently be miniaturized. Since it is necessary to dispose the predetermined distance between the dielectric substrate and the radiation member, it is difficult to reduce a distance between the radiation member and the peripheral circuit, and there is therefore a problem that it is difficult to sufficiently reduce a signal loss.